OK, here are some file sizes for you, to
show you what to expect with different kinds of deinterlacing and DivX compression methods.

I compressed a 42 minute movie with a lot of fast moving
scenes.
I used DivX Professional 5 with "Constant Quality" of 93% (but that's up
to you),
keyframe interval "max every 50 frames", "GMC" and "Bi-directional
Encoding".
I encoded with "No sound", so that the figures below are purely video.

Don't do it. Result looks bad. You lose details and motions are unnatural.
This method is called "(best)" in Virtualdub while in my opinion
it's not, but it's a matter of taste (Please see the 2 swing sample pics
below).

Even "25 fps, resize to 384x288" (8)
is better.

(4)

25 fps720x288

Discard field 1

74.2%

You definitely lose the half info, movie is unfluid, but result is sharp
and saves you about 25%. Only 25%, I might add, because you give up 50% of
resolution and 50% of fluidity.

(5)

25 fps720x288

Discard field 2

75.2%

Interesting: In this movie all odd fields were harder to compress than even
fields.

In my view this is the method of choice, if size matters a bit, but not too much. You get a superfluid movie and the loss of visible information is not too high and you keep your movie 4:3.

This could be the deal for you if size matters a bit.

(8)

25 fps384x288

Resize down to 384x288

36.7%

You size down to about 27% of the original film BUT the movie is kind of
strangly unfluid/blurred. For 27% of the original quality you get 37% size.

In Virtualdub the deinterlace filter "Blend" is the same as
"Resize down" except for the resizing. So you get exactly the same
result, except the Blend'ed picture stays the same size and the downsized
one is a little more blurred of course,
because of the smaller image size.

This could be considered a typical looking movie downloaded from the
internet. A bit unsharp and not fluid, but small.

(9)

25 fps320x240

Discard field 1

29.6%

Resized down to 320x240 after
discarding every second line.

In my view, it's a matter of taste whether you like resizing down (8) or discarding+resizing down
(9). (8) gives you a
blurred picture, (9) gives you a unfluid but sharp
movie. Because it's quite sharp you can resize it down more. (How
can a lower resolution be better?)

But I could agree that (3) and (8)
can give you a good quality if the footage has a lot of static areas (like
news broadcasting).

Once you get
used to its unfluid play you will appreciate the sharper image quality.

I
would say this is for sure the method of choice if you have an NTSC movie, because
the frame rate of NTSC (ca. 30fps) makes the movie more fluent anyway.

And when I say
unfluent for PAL systems (25fps), then this still far better compared to typical internet clips with
15 fps or 12 fps. Shame on you, you internet uploaders.

The difference between (8) and (9)
stays clearly visible even if you resize to small frame sizes, even below 384x288:

Method (9) (Discard)

Method (8) or (3) (Blend or resize down).
You could call these effects "Ghosts".

This deinterlacing method a very good and fast solution:

1)

You work within Virtualdub only, thus very fast, no Avisynth needed.

2)

Discarding is fast.

3)

Resizing is fast, because you resize only the half info after
discarding.

4)

Compressing is fast because you compress a lower height/width.

5)

Height/width ratio is correct

6)

Since most of you will resize the final footage down
anyway, discarding a field (=losing half of the resolution) isn't
that bad.

7)

Leaves you with absolutely no interlacing artefacts.

This could be the "good speed/quality/size ratio" deal for you.

(10)

25 fps720x576

Duplicate Field 2

137.5%

This is the same as "Insert Field2 instead of Field1" thus
doubling your height to keep the original ratio. You will get quality
enhancement because the compression artefacts are much less visible. See all
reasons and drawbacks for resizing
up before encoding.

The same applies here as to (10). The 2 differences to above
are: 50fps, resizing is
bicubic instead of just duplicating.

I would definitely use (11)
instead of (10), because for
15 percentage points more, your quality will be 4 times as good.
The drawback is that your computer may be too slow to decode the
movie. In that case you may use (17) or (18).

Don't do it. You lose a lot of details, compression is slow as hell
(14 hours
for 42 minutes film) and you don't gain much. If "saving filesize thru
smoothing" is really needed, use DivX internal smoothing filters
instead. They are optimized for to save filesize via smoothing.

If you are a quality fan then this could be the best quality deal for you. This filter is unbelievably good, but usually leaves you with twice the filesize (well, not always) and twice the height (=original height). This could make the movie unplayable (PC too slow). Besides the encoding itself is slow.

I love the results though. Brilliant, excellent, the way all video should
look like: Fluent movements, sharp still scenes (backgrounds, unmoving
objects).

To give you an idea, how big files are: I encode my DVB recorded MTV
videos (528x576) with (15) and they are
between 30MB and 170MB each. The filesize is mostly depending upon

a) How sharp is the source material (DivX loves blur).
b) Are there black letterboxes at the top and bottom? (Less to encode).
c) How many movements are there?
d) How dark is the overall video? (DivX loves darkness).

Unbelievable, that this resolution can give you such a sharp picture (but the encoding is quite slow).

Small size, sharp picture, fluent movements. Only
15 percentage points bigger than (9), but at least 4 times the
quality.

This could be the quality/size/fluidity deal for you.

(17)

25 fps720x540

Discard Field 1

99.6%

Discard and resize height up until
width:height matched 4:3

The differences to
method (10) are, that you
resize by Bicubic Resizing instead of just duplicating the lines
and that you resize to a smaller height than (10).
This gives you a better quality as the pictures show (see (11)).
AND: You get the correct aspect ratio. But it's still only 25
frames instead of 50, so I wouldn't use it.

(18)

25 fps720x576

Discard Field 1

109.9%

Discard and resize up by bicubic
resizing to double the height.

The only difference to
method (17) is, that you resize to the same width/height like in (10). This gives you a better picture but still results in a
smaller filesize.

Why use it? Nearly the same
filesize as (15), but not near as good. Use (16) instead,
if you want to decrease filesize effectively while still keeping
very high quality.

This filter leaves you with twice the height (=original
height). This could make the
movie unplayable (PC too slow).

(20)

50 fps720x576

Smart Bob

223.6%

"Smart Bob" filter for
VirtualDub by Donald Graft

Quite good filter. About
twice as fast as (15) but a
little worse quality and a bigger filesize. However in some cases
this filter may produce smaller files than (15).

Now I wanted to check whether it makes a difference HOW I
downsize the movie.

Method

%

Important
Details

1. Resize down (bicubic)

100.0%

resized down to ca.49% by changing the
width only

2. Resize down (bilinear)

97.8%

resized down to ca.49% by changing the
width only

3. Resize down (nearest neighbour)

101.2%

resized down to ca.49% by changing the
width only

4. Resize down/down (bicubic)

97.6%

resized down to ca.49% by changing the
height AND width

1) Because resizing
always blurs it is no wonder, that resizing height AND width
(method 4) blurs
more than width alone and thus results in a lower filesize since
DivX gives you a smaller filesize the more the movie is washed
out.

2) It is interesting, that the differences between the
resizing methods of Virtualdub are nearly invisible (but they are
visible). So I would suggest you use the bilinear method.
Important:
Bilinear resizing can give you strange effects with interlaced
video. So deinterlace your footage first, when you decide to use
it.

3) The best method for quality is bicubic
resizing, which shows the
same quality results, as if you resized by Adobe® Photoshop®.

How do the filesizes compare when using
different compressions = different DivX Quantizers
from the DivX
Compression menu?

Setting the DivX
Quantizer

As you can see from the graphics below from 0% to 80% the file
size
stays about the same, while the quality improves much more. But keep
in mind that everything below 80% can hardly be called "good
quality".

The filesize increases very fast as you add a few more % above
80%.

Above 95% quality doesn't increase too much, while the file
size
jumps up exorbitantly. So there's not much reason to go beyond
95%.

Below 90% quality drops faster than you save bytes. So there's
not much reason to go below 90% either.